CN111175750B - Imaging method and device, device and storage medium for synthetic aperture radar - Google Patents

Abstract

The embodiment of the application discloses an imaging method, an imaging device, equipment and a storage medium of a synthetic aperture radar, wherein the method comprises the following steps: transmitting a plurality of radar signals with non-overlapping frequency spectrums to a mapping band within a pulse repetition time so as to realize simultaneous observation of a plurality of different sub-mapping bands in the mapping band; receiving a plurality of echo signals reflected by the plurality of different sub mapping bands; sequentially performing range-wise frequency spectrum splicing and pulse compression on each of the multiple echo signals to obtain range-wise imaging echo signals; and sequentially carrying out azimuth multi-channel reconstruction and pulse compression on each echo signal of the range direction imaging to obtain a synthetic aperture radar image corresponding to the sub mapping band.

Description

Imaging method and device, device and storage medium for synthetic aperture radar

technical field

The embodiments of the present application relate to, but are not limited to, a synthetic aperture radar (Synthetic Aperture Radar, SAR) technology, and in particular, relate to a synthetic aperture radar imaging method, device, device, and storage medium.

Background technique

So far, many scholars at home and abroad have conducted in-depth research on the High Resolution Wide Swath (HRWS) imaging system of spaceborne SAR, and proposed several common imaging modes, mainly based on variable pulse repetition frequency (Pulse Repetition Frequency). Repetition Frequency, PRF) spaceborne SAR (Staggered-SAR), Displaced Phase Center Multiple Azimuth Beam-Digital Beam Forming-SAR (DPCMAB-DBF-SAR) and single-phase center multiple beam ( Single Phase Center Multiple AzimuthBeam-Digital Beam Forming-SAR, SPCMAB-DBF-SAR) and so on. However, these modes have extremely high requirements on the processing of the echo signal and the system platform, which makes it difficult to design a radar system that meets the SAR performance requirements. The imaging system of the spaceborne HRWS synthetic aperture radar that has been proposed mainly uses the digital beamforming (DBF) technology in the range direction and the Azimuth Multi-channel (AMC) technology in the azimuth direction. For DBF technology, the weights or time delays of the control beams are formed at the baseband. This requires the distortion-free signal transmission in the channel and the consistency of the frequency response of each array element channel. However, the frequency response of multiple channels of the actual system is difficult to meet such strict requirements, which makes it very difficult to apply the DBF technology to the spaceborne HRWS-SAR imaging system.

SUMMARY OF THE INVENTION

In view of this, the embodiments of the present application provide an imaging method, apparatus, device, and storage medium for a synthetic aperture radar.

An embodiment of the present application provides an imaging method for synthetic aperture radar, including: transmitting a plurality of radar signals with non-overlapping spectrums to a swath within one pulse repetition time, so as to realize simultaneous imaging of multiple different sub-swaths in the swath Observing; receiving multiple echo signals reflected by the multiple different sub-swaths; performing range-wise spectrum splicing and pulse compression on each of the multiple echo signals in turn to obtain echo signals of range-wise imaging ; Perform azimuth multi-channel reconstruction and pulse compression on each of the range-imaging echo signals in turn to obtain a synthetic aperture radar image corresponding to the sub-swath.

Embodiments of the present application provide an imaging device for synthetic aperture radar, including: a transmitting module configured to transmit multiple radar signals with non-overlapping spectrums to a swath within one pulse repetition time, so as to realize the detection of multiple radar signals within the swath. different sub-swaths are observed at the same time; a receiving module is used for receiving multiple echo signals reflected by the multiple different sub-swaths; a first processing module is used for sequentially processing each of the multiple echo signals Perform range-direction spectrum splicing and pulse compression to obtain echo signals of range-direction imaging; the second processing module is used to sequentially perform azimuth-direction multi-channel reconstruction and pulse compression on each echo signal of the range-direction imaging to obtain Synthetic Aperture Radar image of the corresponding sub-swath.

Embodiments of the present application provide a computer-readable storage medium, where computer-executable instructions are stored in the computer-readable storage medium, where the computer-executable instructions are configured to perform steps of the methods provided in the foregoing embodiments.

An embodiment of the present application provides an imaging device for synthetic aperture radar, including: a memory and a processor, where the memory stores a computer program that can be executed on the processor, and when the processor executes the program, the above-mentioned embodiments provide steps in the method.

In the embodiment of the present application, multiple radar signals with non-overlapping spectrums are transmitted to the swath within one pulse repetition time, so as to realize simultaneous observation of multiple different sub-swaths in the swath. In this way, when the radar transmits a frequency band signal to illuminate a sub-swath, this radar signal transmission method can remove the interference of the fuzzy energy generated by other frequency bands and suppress the echo signal distance ambiguity ( Blur in the distance direction), improve the imaging resolution, and can solve the problems of complex echo data processing, difficult radar system design and high engineering implementation difficulty.

Description of drawings

FIG. 1 is a schematic diagram of an implementation flowchart of a synthetic aperture radar imaging method provided by an embodiment of the present application;

2 is a signal transmission timing diagram of a high-resolution wide-width SAR system provided by an embodiment of the present application;

FIG. 3 is a schematic diagram of the beam irradiation geometry of the high-resolution wide-width SAR provided by the embodiment of the present application;

4 is a schematic diagram of a radar receiving an echo signal provided by an embodiment of the present application;

FIG. 5 is a receiving sequence diagram of the fifth and sixth echoes in FIG. 4 provided by an embodiment of the present application;

FIG. 6 is a flowchart of range-oriented high-resolution imaging provided by an embodiment of the present application;

FIG. 7 is a flowchart of signal reconstruction of azimuth multi-channel provided by an embodiment of the present application;

8 is a schematic diagram of an aliased azimuth echo signal provided by an embodiment of the present application;

FIG. 9 is a schematic diagram of transmission interference provided by an embodiment of the present application;

10 is a schematic diagram of sub-satellite echo interference provided by an embodiment of the present application;

FIG. 11 is a flow chart of system beam position design provided by an embodiment of the present application;

12 is a schematic diagram of a compressed pulse for implementing range-to-spectrum splicing provided by an embodiment of the present application;

FIG. 13 is a schematic diagram of a compressed pulse of azimuth multi-channel reconstruction provided by an embodiment of the present application;

FIG. 14 two groups of beam position zebra diagrams provided by the embodiments of the present application;

FIG. 15 is a schematic diagram of the composition and structure of an imaging device of a synthetic aperture radar according to an embodiment of the present application;

FIG. 16 is a schematic diagram of a hardware entity of an imaging device of a synthetic aperture radar according to an embodiment of the present application.

Detailed ways

The technical solutions of the present application will be further elaborated below with reference to the accompanying drawings and embodiments.

This embodiment provides a schematic diagram of an implementation flow of a synthetic aperture radar imaging method. As shown in FIG. 1 , the method includes:

Step 101, transmitting a plurality of radar signals with non-overlapping spectrum to the swath within one pulse repetition time, so as to realize simultaneous observation of multiple different sub-swaths in the swath;

Here, the pulse repetition time (PRT) is the inverse of the pulse repetition frequency (Pulse Repetition Frequency, PRF), which is one of the most important characteristic parameters of the pulse radar signal. Pulse repetition frequency is the rate at which pulses or groups of pulses are emitted. That is, the pulse repetition rate is the number of pulses transmitted per second, expressed in Hertz (Hz). Here, the radar signal may be a linear frequency modulation signal (Linear Frequency Modulation, LFM).

The swath is the target area to be measured, and the sub swath is a sub-area of the target area to be measured. The spectrum refers to the spectrum of the radar signal, and the signal can also be decomposed in a certain orthogonal signal space. And the most used quadrature function set in practical application is the trigonometric function set (sine or cosine signal). Any signal, as long as it meets certain conditions, can be decomposed into a linear superposition of a series of sine (or cosine) components of different frequencies; each sine component of a specific frequency has its corresponding amplitude and phase. Therefore, for a signal, the amplitude and phase of its components are functions of frequency respectively; or taken together, its complex amplitude is a function of frequency. This magnitude (or phase) function with respect to frequency is called the spectrum of the signal. The radar signals with non-overlapping frequency spectrums are radar signals with non-overlapping frequencies.

For example, use PRF of 1448HZ to illuminate the target area to be surveyed and mapped, at this time PRT=0.00007s, that is, a radar signal is emitted every 0.00007s to illuminate the target area to be surveyed and mapped, and the illuminated area is the target area to be surveyed and mapped. Sub swath.

Step 102, receiving multiple echo signals reflected from the multiple different sub-swaths;

In the actual process, the sub-swath illuminated by the radar signal will reflect one echo signal, and the radar receives multiple echo signals reflected by different sub-swaths.

For example, in one pulse repetition time, radar signals of 5 different frequency bands are continuously transmitted to the target area to be mapped, B1, B2, B3, B4 and B5. The radar signals of each frequency band illuminate a part of the target area, and each is illuminated The target area is a sub-swath of the target area to be mapped, and each illuminated sub-swath reflects an echo signal to the radar.

Step 103, performing range-wise spectrum splicing and pulse compression on each of the multiple echo signals in sequence to obtain echo signals of range-wise imaging;

Here, the spectrum splicing refers to the spectrum splicing performed in the distance direction of the radar signal, and the spectrum splicing is to determine the power mapping of B(f) and A(f) by using the relationship between the overlapping spectrums A(f) and B(f). The relationship g is to make the difference between the dynamic range and noise floor power of g(B(f)) and A(f) as small as possible, and the junction satisfies the splicing boundary to be smooth and smooth, and the envelope trend is suppressed without changing the carrier. The power relationship between the signals. Commonly used spectrum splicing algorithms include spectrum splicing algorithms based on histogram specification. The pulse compression refers to the modulation of the wide pulse signal, which includes linear frequency modulation, nonlinear frequency modulation and phase encoding, etc., and then pulse compression is performed on the echo wide pulse at the receiving end, and finally narrow pulses are obtained. . Pulse compression can solve the contradiction between the radar operating range and the range resolution, and can ensure that the radar can improve the range resolution under a certain operating distance.

In the actual process, spectrum splicing is performed on the reflected echo signals first, the overlapping spectrum signals are processed, and the range resolution of the echo signals is improved by pulse compression.

Step 104: Perform azimuth multi-channel reconstruction and pulse compression on each of the echo signals imaged in the range direction sequentially to obtain a synthetic aperture radar image corresponding to the sub-swath.

During the operation of the SAR sensor, there are interference factors such as inconsistent channel characteristics, deviation of sampling time, noise, etc., which lead to spectral noise in the reconstructed signal and affect the reconstruction accuracy. Azimuth multi-channel reconstruction technology can restore uniformly sampled signals, reduce spectral noise and improve reconstruction accuracy.

Here, the multi-channel reconstruction is a method of compensating for the phase shift and time shift of the multi-channel echo signals and removing the ambiguous spectral components of each channel to restore the uniformly sampled signal.

In the actual process, after range imaging, the azimuth direction of the echo signal is still the unprocessed echo signal, and the azimuth imaging signal with low spectral noise and high reconstruction accuracy can be obtained by azimuth multi-channel reconstruction and pulse compression.

For example, at the transmitting end, by continuously switching and transmitting multiple radar signals with non-overlapping spectrum within one pulse transmission time to illuminate different target areas, the simultaneous observation of multiple sub-swaths is realized. At the receiving end, multiple azimuth channels continuously receive the echo signals of multiple sub-swaths, and the receiving mode can be time-division multiplexing. In the later data processing, the method of frequency domain filtering is used to effectively suppress the range ambiguity of the echo signal, and the echo data is processed by spectrum splicing in the range and multi-channel reconstruction in the azimuth to obtain a lower range. Blurred, high-resolution wide-format SAR images.

In some embodiments, the plurality of radar signals with non-overlapping spectrums are one group of M groups of different radar signals, and the M radar signals in the group have different frequency bands; wherein M is greater than an integer equal to 1, the M radar signals in the group are arranged in order of spectrum from small to large, the starting frequency of the P-th radar signal is equal to the cut-off frequency of the P-1-th radar signal, where , P is an integer greater than or equal to 2 and less than or equal to M.

Within the current pulse repetition time, a group of radar signals in the M groups are sequentially transmitted to the swath at a specific pulse emission interval and a specific pulse emission time, so as to transmit a group of radar signals (sequences) to the swath; wherein, The set of radar signals includes a plurality of radar signals with non-overlapping frequency bands.

In the embodiment of the present application, multiple radar signals with non-overlapping spectrums are transmitted to the swath within one pulse repetition time, so as to realize simultaneous observation of multiple different sub-swaths in the swath. In this way, when the radar transmits a frequency band signal to illuminate a sub-swath, this radar signal transmission method can remove the interference of the fuzzy energy generated by other frequency bands to it by the method of frequency domain filtering, and suppress the distance ambiguity of the echo signal. The imaging resolution is improved, and the existing echo data processing is relatively complex, the radar system design is relatively difficult, and the engineering implementation is relatively difficult.

This embodiment provides an imaging method for synthetic aperture radar, wherein the multiple radar signals with non-overlapping spectrums are one group of M groups of different radar signals, and the M radar signals in the group have different frequency band; where M is an integer greater than or equal to 1. The method includes:

Step 201, taking the M pulse repetition times as one cycle, cyclically transmitting the M groups of different radar signals, so as to realize simultaneous observation of multiple different sub-swaths in the swath;

Wherein, the plurality of radar signals with non-overlapping spectrums are one of M groups of different radar signals, and the M radar signals in the group have different frequency bands; wherein, M is an integer greater than or equal to 1 ;For example, M=5, taking the five pulse repetition times of PRT1~PRT5 as a cycle, in the signal transmission time of PRT1n~PRT5n (n>1), different radars are cyclically transmitted according to the signal transmission timing of PRT1~PRT5. Signal. Within each of the 5 PRTs, the radar transmits 5 spectrally non-overlapping signals. For example, within a PRT, the radar transmits five radar signals with frequency bands B_1, B_2, B_3, B_4, and B_5, and the spectrums of these five radar signals do not overlap each other.

In some embodiments, the M radar signals in the group are arranged in ascending order of frequency spectrum, the starting frequency of the P-th radar signal is equal to the cut-off frequency of the P-1-th radar signal, Wherein, P is an integer greater than or equal to 2 and less than or equal to M; for example, the five radar signals transmitted satisfy: B_1e=B_2s, B_2e=B_3s, B_3e=B_4s, and B_4e=B_5s. where B_is and B_ie represent the start and end frequencies of the i-th signal, respectively. In PRT1, transmit B_1, B_5, B_4, B_3, and B_2, and transmit in sequence within the pulse transmit time of PRT2, PRT3, PRT4, and PRT5: B_3, B_2, B_1, B_5, and B_4, B_5, B_4, B_3, B_2, and B_1 , B_2, B_1, B_5, B_4 and B_3, B_4, B_3, B_2, B_1 and B_5 signals.

Step 202, receiving multiple echo signals reflected by the multiple different sub-swaths;

Step 203, performing range-wise spectrum splicing and pulse compression on each of the multiple echo signals in sequence to obtain echo signals of range-wise imaging;

Step 204: Perform azimuth multi-channel reconstruction and pulse compression on each of the echo signals imaged in the range direction sequentially to obtain a synthetic aperture radar image corresponding to the sub-swath.

In the embodiment of the present application, the characteristics of the radar signal within a pulse repetition time are constrained, and the cycle period of the pulse repetition time is specified. In this way, the radar signal received by one sub-swath can be shielded from the ambiguous interference from signals of other frequency bands through simple filtering processing, the imaging process of the radar signal can be simplified, and the range-ambiguity signal ratio can be reduced.

This embodiment provides an imaging method for synthetic aperture radar, wherein the multiple radar signals with non-overlapping spectrums are one group of M groups of different radar signals, and the M radar signals in the group have different frequency band; where M is an integer greater than or equal to 1. The method includes:

Step 301: According to the formula X _i =V*T*i, determine the transmitting position of the radar signal of the i-th pulse repetition time in the azimuth direction; wherein X _i is the i-th pulse repetition time in the azimuth direction. the launch position, V represents the instantaneous velocity of the radar moving in the azimuth direction, and T represents the pulse repetition time;

For example, the timing of signal transmission by the satellite at the azimuth coordinate of 0 corresponds to the pulse transmission timing of the first pulse repetition interval of PRT1, and so on, the signal transmission timing of the satellite at the azimuth position Xi (i>1) can be obtained. Among them, Xi=V*PRT*i, V represents the instantaneous velocity of the satellite and PRT represents the pulse repetition time.

Step 302, according to the speed of light C, the pulse repetition time T, and the width Swath of the sub-swath, determine the center slant distance R _ij of the radar signal transmitted from the emission position X _i to the j-th sub-swath;

For example, the center slant distances of the radar illuminating the 5 sub-swaths at the azimuth 0 position are R_1, R_2, R_3, R_4 and R_5 respectively. And, their relationship can be described as formula (3-1). Among them, it is assumed that the pulse repetition time PRT=T of the SAR system, Swath is the width of the sub-swath, and C is the propagation speed of light.

Step 303, on the transmitting position X _i , transmit the radar signal of the ith mod M group to the j th sub swath with the center slant distance R _ij , mod is the symbol of the remainder function, i is an integer greater than or equal to 1, and realize simultaneous observation of multiple different sub-swaths in the swath;

For example, M=5, in the first pulse repetition time, a group of B_1, B_5, B_4, B_3 and B_2 radar signals are transmitted to the sub-swaths, then in the sixth pulse repetition time, 6mod 5 is 1, The radar signal is transmitted to the sub-swaths in the sequence of the radar signal transmitted at the first pulse repetition time.

Step 304, receiving multiple echo signals reflected from the multiple different sub-swaths;

Step 305, performing range-wise spectrum splicing and pulse compression on each of the multiple echo signals in sequence to obtain echo signals of range-wise imaging;

Step 306: Perform azimuth multi-channel reconstruction and pulse compression on each of the echo signals imaged in the range direction sequentially to obtain a synthetic aperture radar image corresponding to the sub-swath.

In the embodiment of the present application, according to the speed of light C, the pulse repetition time T, and the width Swath of the sub-swath, the center slope distance R _ij of the radar signal transmitted from the emission position X _i to the j-th sub-swath is determined . In this way, the beam position of the SAR system can be designed when the system beam is designed.

This embodiment provides an imaging method for synthetic aperture radar, and the method includes:

Step 401: According to the formula X _i =V*T*i, determine the launch position of the radar signal of the i-th pulse repetition time in the azimuth direction; wherein X _i is the i-th pulse repetition time in the azimuth direction. the launch position, V represents the instantaneous velocity of the radar moving in the azimuth direction, and T represents the pulse repetition time;

确定所述发射位置X_i向所述第j个子测绘带发射的雷达信号的中心斜距R_ij；其中，R_i1表示所述发射位置X_i向所述第1个子测绘带发射的雷达信号的中心斜距，C表示光速，Swath表示子测绘带的幅宽；j表示雷达照射第j子测绘带；或者，Step 402, according to

Determine the center slant distance R _ij of the radar signal transmitted from the emission position X _i to the jth sub-swath; wherein, R _i1 represents the distance of the radar signal transmitted from the emission position X _i to the 1st sub-swath. Center slant distance, C is the speed of light, Swath is the width of the sub-swath; j is the radar illumination of the jth sub-swath; or,

确定所述发射位置X_i上发射雷达信号的第j个中心斜距R_ij与发射位置X_i+n上发射雷达信号的第j-n个中心斜距R_(i+n)(j-n)之间的关系；其中，所述n为大于1且小于j的整数；according to

Determine the difference between the jth center slant distance R _ij of the radar signal transmitted at the transmitting position Xi and the jnth center slant distance R _(i+n)(jn) of the radar signal transmitted at the transmitting position X _{i +n} . relationship; wherein, the n is an integer greater than 1 and less than j;

Step 402 describes the relationship of the propagation paths of radar signals illuminating different sub-swaths at different times.

Step 403, at the transmitting position X _i , transmit the radar signal of the i mod M group to the j th sub-swath with the center slant distance R _ij , where i is an integer greater than or equal to 1, so as to realize the detection of the radar signals in the swath. A plurality of different sub-swaths are observed simultaneously, wherein the plurality of radar signals with non-overlapping frequency spectrums are one group of M groups of different radar signals, and the M radar signals in the group have different frequency bands ; where M is an integer greater than or equal to 1, the M radar signals in the group are arranged in order of spectrum from small to large, and the starting frequency of the P-th radar signal is equal to the P-1-th radar signal The cutoff frequency of the signal, where P is an integer greater than or equal to 2 and less than or equal to M;

Step 404, receiving multiple echo signals reflected from the multiple different sub-swaths;

Step 405: Perform frequency-domain filtering on the echo signals of the j sub-swaths respectively to obtain multiple echo signals that eliminate distance ambiguity;

Here, since the bandwidth of the radar signal irradiating a sub-swath is different in different pulse repetition times, the frequency domain filtering method can be used to effectively suppress the range ambiguity of the echo signal.

For example, when the radar receives the echo signal emitted by the radar signal of the frequency band B_4 irradiated on the sub-swath 1, which is transmitted in PRT5, the radar also receives the frequency band B_1, B_3 transmitted by the radar signal in PRT4, PRT3, PRT2 and PRT1. The signals of B_5, B_2 illuminate the blurred signals of the sub-swaths 2, 3, 4 and 5, respectively. By setting the frequency band to B_4, the ambiguity energy generated by the radar signals with frequency bands B_1, B_2, B_3 and B_5 to sub-swath 1 can be filtered out.

Here, it should be noted that the beam position of the radar signal that satisfies step 402, the following formula (4-1) can be used to measure the distance ambiguity of the echo signal:

The subscript n∈{5,6,…,N} is the nth fuzzy echo, N is the number of distance fuzzy areas, G^2(θ) is the two-way antenna pattern, σ^0(θ_n) is the nth The backscattering coefficient of the center of the blurred area, R_n is the distance from the center of the nth blurred area, η_n is the incident angle of the nth blurred area, σ^0(θ_main) is the backscattering coefficient of the beam irradiating the target area, and R_main is the antenna phase The distance from the center to the target, η_main is the incident angle of the antenna beam illuminating the target.

Because in the total distance ambiguity, the echo signals of the 1st, 2nd, 3rd and 4th ambiguity regions occupy a large part of the ambiguity energy. Therefore, the use of the radar signal satisfying step 402 can realize the suppression of the range ambiguity of the echo signal.

Usually, to measure the distance ambiguity of the echo signal, if the performance index value calculated by formula (4-1) is less than -20dB, the performance is good. The calculation of the existing transmission method starts from 1. After the improvement of the sub-swath radar signal transmission method in this embodiment, it can be calculated from 5. The calculated ambiguity degree is smaller than that of the original transmission method, indicating that after the improvement It can suppress the echo signal distance blur, and has the advantage of lower distance blur.

Step 406, performing range-wise spectrum splicing and pulse compression on each of the multiple echo signals in sequence, to obtain echo signals of range-wise imaging;

Step 407: Perform azimuth multi-channel reconstruction and pulse compression on each of the echo signals imaged in the range direction sequentially to obtain a synthetic aperture radar image corresponding to the sub-swath.

和

限定，这样，经过本实施例中子测绘带发射方式的改进，可以减少需要累积求和的回波数，计算出的模糊成度比原有发射方式小，能抑制回波信号距离模糊，性能好，并通过对中心斜距进行几何约束关系得到该高分宽幅成像系统的波束位置。In the embodiment of the present application, the center slant distance of the radar signal is calculated.

and

In this way, after the improvement of the neutron swath transmission method in this embodiment, the number of echoes that need to be accumulated and summed can be reduced, the calculated ambiguity degree is smaller than that of the original transmission method, the distance ambiguity of the echo signal can be suppressed, and the performance is good , and the beam position of the high-resolution wide-format imaging system is obtained by geometrically constraining the center slant distance.

This embodiment provides an imaging method for synthetic aperture radar, and the method includes:

Step 501, transmitting a plurality of radar signals with non-overlapping spectrum to the swath within a pulse repetition time, so as to realize simultaneous observation of multiple different sub-swaths in the swath;

Step 502, receiving multiple echo signals reflected from the multiple different sub-swaths;

Step 503, performing range-wise spectrum splicing and pulse compression on each of the multiple echo signals in sequence to obtain echo signals of range-wise imaging;

Step 504: Perform an azimuth Fourier transform on each echo signal of the range imaging to obtain an aliased echo signal in the frequency domain;

Step 505, using the range beamforming method to filter the azimuthal aliased echo signals of each frequency domain to obtain a Doppler spectrum deblurred in each azimuth direction;

Step 506, performing spectrum splicing on the deblurred Pler spectrum of each azimuth to obtain each complete azimuth Doppler spectrum;

Step 507: Perform azimuth pulse compression on each complete azimuth Doppler spectrum to obtain a synthetic aperture radar image of the corresponding sub-swath.

For example, the azimuth Fourier transform is performed on the echo signal of each sub-band, and the signal is transformed into the frequency domain to obtain the azimuth aliased echo signal; the range beamforming method is used to analyze the echoes of multiple sub-channels. Perform time domain weighting to obtain the deblurred Doppler spectrum; splicing multiple deblurred Doppler spectra in each sub-band to obtain a complete azimuth Doppler spectrum, and perform azimuth pulse compression to obtain the azimuth to high-resolution SAR images.

In the embodiment of the present application, the azimuth Fourier transform is performed on each echo signal of the range imaging to obtain an aliased echo signal in the frequency domain; the range beamforming method is used for each frequency domain. The azimuth aliased echo signal is filtered to obtain the Doppler spectrum deblurred in each azimuth direction; the spectrum splicing is performed on the deblurred Pler spectrum in each azimuth direction to obtain each complete azimuth direction. Pler spectrum; perform azimuth pulse compression on each complete azimuth Doppler spectrum to obtain a synthetic aperture radar image of the corresponding sub-swath. In this way, an azimuthally deblurred high-resolution radar image can be obtained.

The embodiments of the present application relate to a new, effective and easy-to-implement spaceborne HRWS-SAR imaging method. Spaceborne SAR has the characteristics of all-day and all-weather, and can realize functions such as high-resolution imaging, polarization interferometric altimetry and deformation, land vegetation inversion, and moving target detection. So far, many scholars at home and abroad have also conducted in-depth research on the HRWS imaging system of spaceborne SAR, and proposed several common imaging modes, mainly including spaceborne SAR based on variable pulse repetition frequency (PlusRepetition Frequency, PRF) ( Staggered-SAR), offset phase center azimuth multibeam DPCMAB-DBF-SAR and SPCMAB-DBF-SAR, etc. However, these modes have extremely high requirements on the processing of the echo signal and the system platform, which makes it difficult to design a radar system that meets the SAR performance requirements. Based on this background, an embodiment of the present application proposes a multi-strip jump synthetic aperture radar (Multi-Swath Jump SAR) imaging method that can realize HRWS imaging.

The imaging system of the spaceborne HRWS synthetic aperture radar that has been proposed mainly uses the digital beamforming (DBF) technology in the range direction and the Azimuth Multi-channel (AMC) technology in the azimuth direction. For DBF technology, the weights or time delays of the control beams are formed at the baseband. This requires the distortion-free signal transmission in the channel and the consistency of the frequency response of each array element channel. However, the frequency response of multiple channels of the actual system is difficult to meet such strict requirements, which makes it very difficult to apply the DBF technology to the spaceborne HRWS-SAR imaging system. For the azimuth multi-channel technology of spaceborne SAR, its engineering practicability is high. And many spaceborne SAR systems have implemented azimuth multi-channel technology, such as: GaoFen-3, TanDEM-X and Sentinel.

The embodiments of the present application provide a spaceborne HRWS-SAR imaging method, that is, Multi-Swath Jump SAR. At the transmitting end, it mainly irradiates different target areas by continuously switching and transmitting multiple radar signals with non-overlapping spectrum within one pulse transmission time, so as to realize the simultaneous observation of multiple sub-swaths. At the receiving end, multiple azimuth channels continuously receive echo signals of multiple sub-swaths in a time-division multiplexing scheme. In the later data processing, the method of frequency domain filtering is used to effectively suppress the range ambiguity of the echo signal, and the echo data is processed by spectrum splicing in the range and multi-channel reconstruction in the azimuth to obtain a lower range. Blurred, high-resolution wide-format SAR images.

The technical solutions adopted by a synthetic aperture radar imaging method proposed in the embodiments of the present application mainly include:

(1) Simultaneous observation of multiple sub-swaths

In the embodiment of the present application, the simultaneous observation of multiple sub-swaths is realized by continuously switching and transmitting a plurality of radar signals with non-overlapping spectrums within one pulse emission time to illuminate different target areas. As shown in FIG. 2 , the horizontal axis in the figure represents the incident angle, different incident angles correspond to different sub-swaths (referred to as sub-bands in the drawings in this application), and the vertical axis represents the pulse emission time in the azimuth direction. In order to make each target object have signals from B1 to B5 to irradiate it, the radar transmits signals of B_1, B_5, B_4, B_3 and B_2 in five different frequency bands in sequence in PRT1 to illuminate the target area respectively: Swath_1, Swath_2, Swath_3 , Swath_4 and Swath_5, where Swath is the width of the sub-swath, which are sequentially transmitted during the pulse transmission time of PRT2, PRT3, PRT4 and PRT5: B_3, B_2, B_1, B_5 and B_4; B_5, B_4, B_3, B_2 and B_1 ; B_2, B_1, B_5, B_4 and B_3; B_4, B_3, B_2, B_1 and B_5 signals illuminate 5 sub-swaths respectively. After that, the transmission timing of the signal repeats the transmission timing of PRT1~PRT5, that is, in the signal transmission time of PRT1n~PRT5n (n>1), different radar signals are cyclically transmitted according to the signal transmission timing of PRT1~PRT5, and irradiate 5 subsections. Mapping strip.

FIG. 3 is a schematic diagram of the beam irradiation geometry of the high-resolution wide-width SAR provided by the embodiment of the present application. As shown in FIG. 3 , when the satellite is at the 0 position in the azimuth, the height is h1 and the timing of the transmission signal corresponds to the pulse transmission timing of PRI1 , continuously switch and transmit 5 radar signals with non-overlapping spectrum to illuminate 5 sub-swaths respectively, and so on, the radar imaging process of the satellite at the position of X _i (i>1) can be obtained. Wherein, X _i =V*PRT*i, V represents the instantaneous velocity of the satellite, and PRT represents the pulse repetition time.

(2) Suppressing distance blur

The system achieves the suppression of the range ambiguity of echo signals by continuously switching and transmitting multiple radar signals with non-overlapping spectrums to illuminate different sub-swaths. In Figure 3, it is assumed that the center slant distances of the five sub-swaths illuminated by the satellite at the azimuth direction of 0 are R_1, R_2, R_3, R_4 and R_5, respectively. And, their relationship can be described as formula (6-1). Among them, it is assumed that the pulse repetition time PRT=T of the SAR system, Swath is the width of the sub-swath, and C is the propagation speed of light.

It is assumed that the moment when the SAR transmits the radar signal at the positions of X ₁ , X ₂ . . . is t_1, t_2, t_3 . . . And it is assumed that the signals irradiating the 5 sub-swaths are B_i1, B_i2, B_i3, B_i4 and B_i5, where i∈{1,2,3,4,…} represents the subscript of the time t _i in the azimuth direction of the emitted radar signal . Then the relationship of the propagation paths of radar signals illuminating different sub-swaths at different times can be described as formulas (6-2) and (6-3). where R _ij represents the two-way propagation path of the B _ij signal, and j represents the radar illumination of the jth sub-swath.

On the premise of satisfying the above relationship, the echo signal as shown in FIG. 4 can be obtained. The radar signals intersecting with the same arc are continuously received in the same PRT, and the receiving timing of the echo signals corresponding to the fifth and sixth arcs (referred to as echoes in each figure of this application) is shown in Figure 5 As shown, the fuzzy signals of PRT1-4 are received in the echo receiving window of PRT5 in sub-swath 1, which will cause distance ambiguity to PRT5. Because the echo signals of PRT1-4 and the echo signals of PRT5 are in different frequency bands, the distance blur can be eliminated by filtering in the frequency domain.

Then it can be seen that the distance ambiguity of the echo signal of the satellite irradiating the jth sub-swath at the i-th position (i>4) is mainly due to the satellite irradiating the j-th sub-swath at the i-1, i-2, i-3... positions. The side lobes of the antenna pattern irradiate the interference of the echo signals of the j+1, j+2, j+3... sub-swaths. Since the radar signal of the satellite irradiating the jth sub-swath at the ith, i+1, i+2... positions in the azimuth direction is the cycle of B_1, B_3, B_5, B_2 and B_4, then the echo signal of each sub-swath is equal to The blurring energy of the 1st, 2nd, 3rd and 4th distance blurred regions can be removed by frequency domain filtering. Therefore, the Range Ambiguity Signal Ratio (RASR) of the HRWS system can be described as formula (6-4).

The subscript n∈{5,6,…,N} is the nth ambiguity echo, N is the number of distance ambiguities, G ² (θ) is the two-way antenna pattern, σ ⁰ (θ _n ) is the nth ambiguity The backscattering coefficient at the center of the area, _Rn is the distance from the center of the _nth blurred area, ηn is the incident angle of the nth blurry area, σ ⁰ (θ _main ) is the backscatter coefficient of the target area illuminated by the beam, and R _main is The distance from the antenna phase center to the target, η _main is the incident angle of the antenna beam illuminating the target.

Because in the total distance ambiguity, the echo signals of the 1st, 2nd, 3rd and 4th ambiguity regions occupy a large part of the ambiguity energy. Therefore, the imaging method can suppress the range blur of the echo signal.

(3) High-resolution imaging in the distance direction

The range-to-high-resolution imaging process of the system is shown in Figure 6. The range imaging process mainly includes 4 parts: 1) echo signals of non-overlapping sub-swaths can be obtained when the geometric relationship described by the above formula is satisfied; 2) the obtained echo signals are filtered and removed in the frequency domain Range ambiguity; 3) The echo signals of 5 sub-bands of a single sub-swath are obtained in 5 consecutive PRTs; 4) The 5 sub-band signals are spliced in the frequency domain, and pulse compression can be used to obtain high range resolution. rate SAR images.

(4) High-resolution imaging in azimuth

Assume that the azimuth Doppler bandwidth of the _HRWS -SAR system is BP and the azimuth oversampling ratio is 1.2. Then PRF of the whole system=1.2B _P , PRF ^′ of each sub-band signal=0.24B _P . Therefore, none of the five sub-band signals can satisfy the Nyquist sampling law and are in an under-sampling state. In order to achieve sufficient sampling of each sub-band signal, azimuth multi-channel technology can be used to reconstruct the azimuth echo signal, and azimuth pulse compression can be performed to obtain azimuth high-resolution SAR images.

The signal reconstruction process of azimuth multi-channel is shown in Figure 7. It mainly includes 3 parts: 1) Transform the signal to the frequency domain to obtain the aliased azimuth echo signal, as shown in Figure 8, when the oversampling rate of 1.2 times is used, when the sampling rate is insufficient, (the The sampling rate is 0.24PRF, which does not satisfy the Nyquist sampling theorem, and the aliasing phenomenon of the spectrum will occur in the azimuth direction.) Using a multi-channel method, there are 5 receiving antennas along one azimuth direction to receive signals respectively, and the figure is obtained. The azimuth echo signal shown; 2) use the range beamforming method to weight the echoes of multiple sub-channels to obtain the deblurred Doppler spectrum; 3) splicing the deblurred Doppler spectrum to obtain Complete azimuth Doppler spectrum, and perform azimuth pulse compression to obtain azimuth high-resolution SAR images.

(5) The beam position design of the system

According to the satellite orbit height, viewing angle (incidence angle) range, imaging width and beam overlap ratio required by the user, the near-end viewing angle, far-end viewing angle and beam width of the beam position of the SAR system can be designed.

The design of the beam position of the synthetic aperture radar system needs to select the PRF, and the selection of the PRF should avoid the influence of the transmission interference (shown in Figure 9) and the sub-satellite echo interference (shown in Figure 10). As shown, the beam width is the width of the illuminated area between the near-end and far-end views, and the sub-satellite point length is the distance from the satellite to the center of the earth and the intersection of the earth's surface and the satellite. As shown in FIG. 10 , a schematic diagram of the sub-satellite echo interference provided by the embodiment of the present application, the beam illuminates the two-way slant range of perigee within one pulse transmission time, and the echo signal received in the PRT includes the sub-satellite point reflection The dashed curve part is the echo signal from perigee to apogee in Figure 9, and the rectangle contained in it is the echo of the sub-satellite point. It can be seen that the echo of the sub-satellite point will interfere with the received echo signal. .

Among them, the emission interference refers to the fact that the transceiver sharing of the synthetic aperture radar antenna causes the radar to fail to receive the effective echo signal within the signal transmission time. In spaceborne SAR, the distance between the antenna phase center and the irradiated target is very far, so that the echo signal always returns to the radar receiving end after several pulses. This may cause the echo signal of the target to fall within the signal transmission time of the SAR, resulting in the loss of effective information.

As can be seen from Figure 9, in order to avoid transmission interference, the effective echoes must fall within the same PRF and cannot overlap with the transmission pulse. Therefore, if the echo signal of the first transmitted pulse returns to the receiver after the nth pulse, then it must satisfy Equation (6-5).

Where T _p is the width of the transmitted pulse, T _near and T _far are the propagation delays corresponding to the two-way slant distances of the beam irradiating perigee and apogee, respectively, and PRF is the pulse repetition frequency.

Among them, the sub-satellite point refers to the sub-satellite point of the satellite, which is the intersection of the connecting line between the satellite and the center of the earth and the surface of the earth. Sub-satellite point echo interference refers to: the echo signal reflected from the sub-satellite point of the satellite interferes with the echo signal reflected from the surveying swath. Therefore, the selection of the PRF of the SAR system needs to avoid the simultaneous arrival of the sub-satellite point echo and the effective echo signal to the receiver. As shown in Figure 10, if the current sub-satellite point echo and the echo of the radar signal transmitted before the mth (m=0, 1, 2...) pulse arrive at the receiver at the same time, the following formula (6-6) needs to be Satisfaction, where T _nadir represents the echo delay of the sub-satellite point.

The zebra diagram of the SAR system can be obtained according to the emission interference and the sub-satellite point echo interference, and then according to the geometric constraint relationship (formulas (6-2) and (6-3)) in the summary of the invention (6-2), and using such as The beam position design flow chart of the traditional SAR system shown in Figure 11 can obtain the beam position of the HRWS-SAR system. By designing the system, the system design parameters output by formulas (6-2) and (6-3) are added to enter the After the system, the distance blur is expressed as Equation (6-4).

In order to avoid sub-satellite point echo interference and emission interference, the beam position of the SAR system needs to be designed, as shown in Figure 11. The design process is as follows:

Step 1101: Design the performance requirements of the SAR system, wherein the performance requirements of the system include system resolution, mapping width, noise equivalent backscatter coefficient (Noise Equivalent Sigma Zero, NESZ), ambiguity requirements, power supply capability requirements and volume weight Require;

Step 1102: Design system parameters according to the performance requirements of the designed SAR system;

Design the transmission bandwidth of the system according to the resolution set by the system; design the upper limit of the azimuth antenna length according to the system resolution and NESZ; design the lower limit of the pulse repetition frequency according to the system resolution and the ambiguity requirements of the system; according to the mapping width and NESZ The upper limit of the azimuth antenna length is required to be designed; the upper limit of the pulse repetition frequency is set according to the surveying and mapping width and ambiguity requirements; the antenna size is designed according to the power supply capability requirements and the azimuth antenna length and volume weight requirements.

Step 1103: Analyze system ambiguity and antenna gain performance according to the pulse repetition frequency and antenna size in the system design parameters;

Step 1104: Determine whether the system ambiguity meets the system design or task requirements;

When the system design or mission requirements are met, the NESZ of the system is analyzed according to the ambiguity of the system, the antenna gain of the first system and the transmission bandwidth;

When the system design or mission requirements are not met, adjust the system antenna size to obtain the second system antenna gain;

Step 1105: Analyze the NESZ of the system according to the ambiguity of the system, the antenna gain of the second system and the transmission bandwidth;

Step 1106: Determine the system parameters, and judge whether the system NESZ meets the system design or task requirements;

When the system design or task requirements are met, output system design parameters;

When the system design or task requirements are not met, modify the system performance requirements and modify the system design parameters according to the system performance requirements, and repeat steps 1101 to 1106 to obtain the output system design parameters.

The synthetic aperture radar imaging method proposed in the embodiments of the present application realizes simultaneous observation of multiple sub-swaths by continuously switching and transmitting multiple radar signals with non-overlapping spectrums within one pulse transmission time to illuminate different target areas. At the receiving end, multiple azimuth channels continuously receive echo signals of multiple sub-swaths in a time-division multiplexing scheme. In the later data processing, the range-direction frequency domain filtering method is used to effectively suppress the range blur of the echo signal, and the echo data is processed by the range-direction spectrum splicing and the azimuth-direction multi-channel reconstruction technology to obtain a better signal. Low-range blur and high-resolution wide-format SAR images have strong engineering achievability. Since the HRWS-SAR system does not use the range DBF technology, the difficulty of engineering realization is reduced. Meanwhile, the azimuth multi-channel technology is very mature, which can be easily applied to the HRWS-SAR system. This also shows that the spaceborne HRWS-SAR system has strong engineering achievability.

For example, a simulation experiment is carried out using the system parameters of a spaceborne SAR. Table 1 shows the system parameters of the spaceborne SAR system in the simulation experiment. The SAR system is subjected to high-resolution imaging in range, multi-channel reconstruction in azimuth, and Beam position design of the system.

Table 1 System parameters of the spaceborne SAR system

track height 670Km Antenna area 10m*3m Antenna carrier frequency 1.26GHz Antenna efficiency 80% duty cycle 20% Azimuth channel number 1T/5R Pulse Width 20us Protection pulse width 2us subsatellite pulse 2us PRF range 1100～2000Hz Viewing angle range 12～62° bandwidth 150MHz

(1) High-resolution imaging in the distance direction

According to the high-resolution imaging flow chart in the range direction in FIG. 6 , the high-resolution imaging in the range direction of the HRWS-SAR system can be realized. The results of the simulation experiments are shown in Figure 12 and Table 2. Table 2 shows the PSLR/ISLR/main lobe width of the compressed pulse in Figure 12. It can be seen that in the distance direction, the unspliced signal and the spectrum spliced signal are much narrower than the original signal after spectrum splicing. Combining with the main lobe width column in Table 2, it can be seen that the spectrum spliced signal is much narrower than the original signal. The main lobe width is changed from 9.2 to 2, indicating that the main lobe width in the distance direction is smaller, the resolution is higher, and the image in the distance direction is clearer. Compared with the case without splicing, the resolution of compressed pulses after range-wise spectrum splicing is improved by about 5 times. It can be seen that the HRWS-SAR system can obtain range-wise high-resolution SAR by means of range-wise spectrum splicing. image.

Table 2 PSLR/ISLR/Main lobe width of compressed pulses in Fig. 12

Attributes PSLR(dB) ISLR(dB) Main lobe width (m) no stitching -13.2668 -9.4502 9.2000 Spectral stitching -13.3200 -8.8082 2 (the ratio to 9.2 is 0.2174)

(2) Multi-channel reconstruction in azimuth direction

According to the azimuth multi-channel signal reconstruction flowchart shown in FIG. 7 , the azimuth reconstruction of the echo signal can be realized, and a SAR image with high azimuth resolution can be obtained. The spectrum of the azimuth aliasing of the echo signals of the system is shown in Figure 8. It can be seen from Figure 8 that the echo signals of the SAR system will receive multiple echo signals in the azimuth direction, and the received echo signals will mixed up. The experimental simulation results obtained by using the azimuth multi-channel technology are shown in Figure 13. The spaceborne radar transmits signals of different bandwidths in sequence, illuminates the target object, and performs azimuth multi-channel reconstruction and pulse compression on the image to obtain the azimuth high-resolution image shown in Figure 13. Among them, Fig. 13 (1) shows the comparison of the signal spectrum of the azimuth multi-channel reconstruction and the reference signal spectrum, the frequency of the reconstructed signal is concentrated in -1500HZ to 1500HZ, and the amplitude value is concentrated in 150 to 200; The frequency is also concentrated in -1500HZ to 1500HZ, and the amplitude value is also concentrated in 150 to 200. The reconstructed signal spectrum is basically the same as that of the reference signal. Figure 13 (2) shows the result of the compressed pulses of two signals subjected to matched filtering. The horizontal axis is the relative time. It can be seen that the amplitude value is the largest at 0, and the resolution of the image is the highest at the maximum amplitude. The image is clearer.

It can be seen that the use of azimuth multi-channel technology can solve the problem of azimuth signal undersampling, realize the deblurring of the azimuth Doppler spectrum, and obtain azimuth high-resolution SAR images.

(3) The beam position design of the system

Based on the system parameters in Table 1, the system beam position design flow chart shown in Fig. 11 and the geometric constraints described above (formulas (6-2) and (6-3)), the HRWS-SAR system beam can be realized location design. The results of designing the two sets of beam positions of the system are shown in Figure 14 and Table 3, where Table 3 shows the parameters of the two sets of beam positions in Figure 14 (1) and Figure (2), and Inci_Near and Inci_Far are respectively Incidence angles at the near and far ends. It can be seen that although the design of the beam position of the system adds additional constraints (formulas (6-2) and (6-3)) compared to the traditional SAR, the beam position that meets the performance requirements of the SAR system can still be designed . The data in (1) in Figure 14 corresponds to the first group in Table 3, and the data in (2) corresponds to the second group in Table 3. It can be seen that the first four columns contain five different sub-swaths, and when PRF=1520Hz , the 5 sub-swaths can be irradiated. When irradiated in this way, the distance is blurred as in formula (6-4), and the performance is good. The last four columns are irradiated with PRF=1448Hz, and the performance can also be optimized.

Table 3 Parameters of two groups of beam positions

First group Inci_Near(deg) Inci_Far(deg) PRF(Hz) 1 12.2485 16.2818 1520 2 35.3668 36.6146 1520 3 46.0909 46.8731 1520 4 53.2980 53.8629 1520 5 58.6808 59.1188 1520 Second Group Inci_Near(deg) Inci_Far(deg) PRF(Hz) 1 16.2818 20.3299 1448 2 37.5752 39.0660 1448 3 48.0824 49.0266 1448 4 55.1743 55.8579 1448 5 60.4741 61.0043 1448

Based on the foregoing embodiments, the embodiments of the present application provide an imaging device for synthetic aperture radar. The device includes each module included and each submodule included in each module, which can pass through a synthetic aperture radar imaging device. Of course, it can also be implemented by a specific logic circuit; in the process of implementation, the processor can be a central processing unit (CPU), a microprocessor (MPU), a digital signal processor (DSP) or a field-available processor. Programming Gate Arrays (FPGA), etc.

FIG. 15 is a schematic structural diagram of a data synchronization apparatus according to an embodiment of the present application. As shown in FIG. 15 , the apparatus 150 includes a transmitting module 151, a receiving module 152, a first processing module 153 and a second processing module 154, wherein: the transmitting module 151, for transmitting a plurality of radar signals with non-overlapping spectrum to the swath within one pulse repetition time, so as to realize simultaneous observation of multiple different sub-swaths in the swath; the receiving module 152, for receiving the said swath; Multiple echo signals reflected from multiple different sub-swaths; the first processing module 153 is used to sequentially perform range spectrum splicing and pulse compression on each of the multiple echo signals to obtain the echo signals of range imaging. wave signal; the second processing module 154 is configured to sequentially perform azimuth multi-channel reconstruction and pulse compression on each echo signal of the range imaging to obtain a synthetic aperture radar image corresponding to the sub-swath.

Based on the foregoing embodiment, wherein the plurality of radar signals with non-overlapping spectrums are one group of M groups of different radar signals, and the M radar signals in the group have different frequency bands; wherein M is an integer greater than or equal to 1, the M radar signals in the group are arranged in order of spectrum from small to large, the starting frequency of the P-th radar signal is equal to the cut-off frequency of the P-1-th radar signal , where P is an integer greater than or equal to 2 and less than or equal to M; an embodiment of the present application provides an imaging device for synthetic aperture radar, the device includes a transmitting module, a receiving module, a first processing module and a second processing module, wherein :

The transmitting module is also used for cyclically transmitting the M groups of different radar signals with M times of the pulse repetition time as a cycle, so as to realize the simultaneous observation of multiple different sub-swaths in the swath; the receiving module , used to receive multiple echo signals reflected from the multiple different sub-swaths; the first processing module is used to sequentially perform range-to-spectrum splicing and pulse compression on each of the multiple echo signals to obtain The echo signal of the range imaging; the second processing module is used for successively performing azimuth multi-channel reconstruction and pulse compression on each echo signal of the range imaging to obtain the synthetic aperture radar image corresponding to the sub-swath.

In some embodiments, the transmitting module includes a first determining sub-module, a second determining sub-module and a transmitting sub-module, wherein:

The first determination sub-module is used to determine the launch position of the radar signal of the i-th pulse repetition time in the azimuth direction according to the formula X _i =V*T*i; wherein, X _i is the i-th pulse repetition time at the launch position in the azimuth direction, V represents the instantaneous velocity of the radar moving in the azimuth direction, and T represents the pulse repetition time;

The second determination sub-module is configured to determine the center slant distance of the radar signal transmitted from the emission position X _i to the jth sub-swath according to the speed of light C, the pulse repetition time T, and the width Swath of the sub-swath R _ij ;

The transmitting sub-module is used to transmit the radar signal of the imod M group to the jth sub-swath with the center slant distance R _ij at the emission position X _i , where i is an integer greater than or equal to 1, so as to realize the detection of the swath of the swath. Multiple different sub-swaths within the swath are observed simultaneously.

确定所述发射位置X_i向所述第j个子测绘带发射的雷达信号的中心斜距R_ij；其中，R_i1表示所述发射位置X_i向所述第1个子测绘带发射的雷达信号的中心斜距，C表示光速，Swath表示子测绘带的幅宽；j表示雷达照射第j子测绘带；或者，根据

确定所述发射位置X_i上发射雷达信号的第j个中心斜距R_ij与发射位置X_i+n上发射雷达信号的第j-n个中心斜距R_(i+n)(j-n)之间的关系；其中，所述n为大于1且小于j的整数。In some embodiments, the second determination sub-module is further configured to

Determine the center slant distance R _ij of the radar signal transmitted from the emission position X _i to the jth sub-swath; wherein, R _i1 represents the distance of the radar signal transmitted from the emission position X _i to the 1st sub-swath. Center slant distance, C represents the speed of light, Swath represents the width of the sub-swath; j represents the radar illuminates the jth sub-swath; or, according to

Determine the difference between the jth center slant distance R _ij of the radar signal transmitted at the transmitting position Xi and the jnth center slant distance R _(i+n)(jn) of the radar signal transmitted at the transmitting position X _{i +n} . relation; wherein, the n is an integer greater than 1 and less than j.

In some embodiments, the second processing module includes a Fourier transform sub-module, a filtering sub-module, a spectral splicing sub-module and a pulse compression sub-module, wherein:

The Fourier transform sub-module is used for performing azimuth Fourier transform on each echo signal of the range imaging to obtain the aliased echo signal in the frequency domain; the filtering sub-module is used for using the range beam The forming method filters the azimuthally aliased echo signals in each frequency domain to obtain a deblurred Doppler spectrum in each azimuth; a spectrum splicing sub-module is used to deblur each azimuth Perform spectrum splicing to obtain each complete azimuth Doppler spectrum; the pulse compression sub-module is used to perform azimuth pulse compression on each complete azimuth Doppler spectrum to obtain the corresponding Synthetic Aperture Radar image of the sub-swath.

The descriptions of the above apparatus embodiments are similar to the descriptions of the above method embodiments, and have similar beneficial effects to the method embodiments. For technical details not disclosed in the device embodiments of the present application, please refer to the descriptions of the method embodiments of the present application for understanding.

It should be noted that, in the embodiment of the present application, if the above-mentioned imaging method for synthetic aperture radar is implemented in the form of a software function module and sold or used as an independent product, it can also be stored in a computer-readable storage in the medium. Based on such understanding, the technical solutions of the embodiments of the present application may be embodied in the form of software products in essence or the parts that contribute to related technologies. The computer software products are stored in a storage medium and include several instructions to make A synthetic aperture radar imaging device (which may be an electronic device such as a personal computer, a server, etc.) executes all or part of the methods described in the various embodiments of the present application. The aforementioned storage medium includes: a U disk, a removable hard disk, a read only memory (Read Only Memory, ROM), a magnetic disk or an optical disk and other mediums that can store program codes. As such, the embodiments of the present application are not limited to any specific combination of hardware and software.

Correspondingly, an embodiment of the present application provides an imaging device for synthetic aperture radar, including a memory and a processor, where the memory stores a computer program that can be run on the processor, and the processor implements the above implementation when executing the program The steps in the method provided in the example.

Correspondingly, the embodiments of the present application provide a computer-readable storage medium on which a computer program is stored, and when the computer program is executed by a processor, implements the steps in the methods provided in the foregoing embodiments.

It should be pointed out here that the descriptions of the above storage medium and device embodiments are similar to the descriptions of the above method embodiments, and have similar beneficial effects to the method embodiments. For technical details not disclosed in the embodiments of the storage medium and device of the present application, please refer to the description of the method embodiments of the present application to understand.

It should be noted that FIG. 16 is a schematic diagram of a hardware entity of a synthetic aperture radar imaging device in an embodiment of the application. As shown in FIG. 16 , the hardware entity of the device 160 includes: a processor 161 , a communication interface 162 and memory 163, where

The processor 161 generally controls the overall operation of the device 160 .

The communication interface 162 enables the device to communicate with other terminals or servers over a network.

The memory 163 is configured to store the instructions and applications executable by the processor 161, and can also cache the data to be processed or processed by each module in the processor 161 and the device 160. Memory, RAM) implementation.

It is to be understood that reference throughout the specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic associated with the embodiment is included in at least one embodiment of the present application. Thus, appearances of "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily necessarily referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments. It should be understood that, in various embodiments of the present application, the size of the sequence numbers of the above-mentioned processes does not mean the sequence of execution, and the execution sequence of each process should be determined by its functions and internal logic, and should not be dealt with in the embodiments of the present application. implementation constitutes any limitation. The above-mentioned serial numbers of the embodiments of the present application are only for description, and do not represent the advantages or disadvantages of the embodiments.

It should be noted that, herein, the terms "comprising", "comprising" or any other variation thereof are intended to encompass non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements, It also includes other elements not expressly listed or inherent to such a process, method, article or apparatus. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in a process, method, article or apparatus that includes the element.

In the several embodiments provided in this application, it should be understood that the disclosed apparatus and method may be implemented in other manners. The device embodiments described above are only illustrative. For example, the division of the units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components may be combined, or Can be integrated into another system, or some features can be ignored, or not implemented. In addition, the coupling, or direct coupling, or communication connection between the components shown or discussed may be through some interfaces, and the indirect coupling or communication connection of devices or units may be electrical, mechanical or other forms. of.

The unit described above as a separate component may or may not be physically separated, and the component displayed as a unit may or may not be a physical unit; it may be located in one place or distributed to multiple network units; Some or all of the units may be selected according to actual needs to achieve the purpose of the solution in this embodiment.

In addition, each functional unit in each embodiment of the present application may all be integrated into one processing unit, or each unit may be separately used as a unit, or two or more units may be integrated into one unit; the above integration The unit can be implemented either in the form of hardware or in the form of hardware plus software functional units.

Those of ordinary skill in the art can understand that all or part of the steps of implementing the above method embodiments can be completed by program instructions related to hardware, the aforementioned program can be stored in a computer-readable storage medium, and when the program is executed, the execution includes: The steps of the above method embodiments; and the aforementioned storage medium includes: a removable storage device, a read only memory (Read Only Memory, ROM), a magnetic disk or an optical disk and other media that can store program codes.

Alternatively, if the above-mentioned integrated units of the present application are implemented in the form of software function modules and sold or used as independent products, they may also be stored in a computer-readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present application may be embodied in the form of software products in essence or the parts that contribute to related technologies. The computer software products are stored in a storage medium and include several instructions to make One device executes all or part of the methods described in the various embodiments of the present application. The aforementioned storage medium includes various media that can store program codes, such as a removable storage device, a ROM, a magnetic disk, or an optical disk.

The above is only the embodiment of the present application, but the protection scope of the present application is not limited to this. Covered within the scope of protection of this application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims (9)

1. A method of imaging a synthetic aperture radar, the method comprising:

taking M pulse repetition times as a period, circularly transmitting M groups of different radar signals so as to realize simultaneous observation of a plurality of different sub-swaths in the swath; wherein one of the M different sets of radar signals comprises a plurality of spectrally non-overlapping radar signals; m radar signals within the group have different frequency bands therebetween; m is an integer greater than or equal to 1;

receiving a plurality of echo signals reflected by the plurality of different sub mapping bands;

sequentially carrying out range spectrum splicing on each echo signal in the plurality of echo signals, and then carrying out pulse compression to obtain an echo signal of range imaging;

and sequentially carrying out azimuth multi-channel reconstruction and pulse compression on each echo signal of the range direction imaging to obtain a synthetic aperture radar image corresponding to the sub mapping band.

2. The method according to claim 1, wherein the M radar signals in the group are arranged in the order of small to large frequency spectrum, the starting frequency of the pth radar signal is equal to the cut-off frequency of the pth-1 radar signal, where P is an integer greater than or equal to 2 and less than or equal to M;

correspondingly, the cyclically transmitting M groups of different radar signals with M pulse repetition times as a period includes: within a pulse repetition time, M radar signals within a group are transmitted according to a specific timing.

3. The method of claim 1, wherein said cyclically transmitting said M different sets of radar signals with M said pulse repetition times as a cycle comprises:

according to the formula

Determining the transmitting position of the radar signal of the ith pulse repetition time in the azimuth direction; wherein,

is the transmit position of the ith pulse repetition time in the azimuth direction,

representing the instantaneous velocity of the radar moving in said azimuthal direction,

representing the pulse repetition time;

according to the light speed C, the pulse repetition time T and the width of the sub mapping band

Determining the transmission position

To the first

Center slope distance of radar signal emitted by sub mapping strip

；

At the emission position

At a center slant distance

And transmitting an i mod M group radar signal to a j sub mapping band, wherein i is an integer greater than or equal to 1.

4. The method of claim 3, wherein the sub swath width is determined according to speed of light C, pulse repetition time T, and sub swath width

Determining the transmission position

To the first

Center slope distance of radar signal emitted by sub mapping strip

The method comprises the following steps:

according to

Determining the transmission position

To the first

Center slope distance of radar signal emitted by sub mapping strip

(ii) a Wherein,

indicating the emission location

To the first

The center slope distance of the radar signal transmitted by each sub mapping strip, C represents the speed of light,

representing the breadth of the sub mapping band; j represents the jth sub-swath irradiated by the radar; or,

according to

Determining the transmission position

J-th center slope of upper-emission radar signal

And a transmitting position

J-n center slant range of upper emission radar signal

The relationship between; wherein n is an integer greater than 1 and less than j.

5. The method of claim 4, wherein before the performing range-wise spectral stitching and pulse compression on each of the plurality of echo signals in sequence to obtain range-wise imaged echo signals, the method further comprises:

and respectively carrying out frequency domain filtering on the echo signals of the j sub mapping bands to obtain a plurality of echo signals with the distance ambiguity eliminated.

6. The method according to claim 1, wherein the sequentially performing azimuth multi-channel reconstruction and pulse compression on each of the range-wise imaged echo signals to obtain a synthetic aperture radar image of a corresponding sub-swath comprises:

performing azimuth Fourier transform on the echo signal of each range direction imaging to obtain an aliasing echo signal of a frequency domain;

filtering the azimuth aliasing echo signal of each frequency domain by using a range beam forming method to obtain a deblurred Doppler frequency spectrum of each azimuth;

performing frequency spectrum splicing on the deblurred Doppler frequency spectrum of each azimuth direction to obtain a complete azimuth direction Doppler frequency spectrum;

and performing azimuth pulse compression on each complete azimuth Doppler frequency spectrum to obtain the synthetic aperture radar image of the corresponding sub mapping band.

7. An imaging apparatus of a synthetic aperture radar, the apparatus comprising:

the transmitting module is used for circularly transmitting M groups of different radar signals by taking M pulse repetition times as a period so as to realize simultaneous observation of a plurality of different sub-swaths in the swath; wherein one of the M different sets of radar signals comprises a plurality of spectrally non-overlapping radar signals; m radar signals within the group have different frequency bands therebetween; m is an integer greater than or equal to 1;

the receiving module is used for receiving a plurality of echo signals reflected by the plurality of different sub mapping bands;

the first processing module is used for sequentially carrying out range-direction frequency spectrum splicing on each echo signal in the plurality of echo signals and then carrying out pulse compression to obtain an echo signal of range-direction imaging;

and the second processing module is used for sequentially carrying out azimuth multi-channel reconstruction and pulse compression on each range-direction imaging echo signal to obtain a synthetic aperture radar image corresponding to the sub mapping band.

8. An imaging device of a synthetic aperture radar comprising a memory and a processor, the memory storing a computer program executable on the processor, characterized in that the processor realizes the steps of the method of any one of claims 1 to 6 when executing the program.

9. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 6.

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